1) you have 1% solution, so you canNOT get 0.0015 mM just from V1/V2!!!2) use simply c1V1 = c2V2, you just need to keep the units of concentration (c1 and c2) the same, i.e. either % or M, but do not mix it!

yes i noticed that mistake but i was so confused let people see where i was going wrong ... umm can u explain that formula u gave though in a bit more detail (or e.g.) because i've never seen it? or heard of it? thanks!

c1v1=c2v2When calculating a concentration if you multiply the volume of original solution used (v1) by its concentration (c1) it is equal to the final concentartion (c2) time the final volume (v2)i.e:if you mix 1ml(v1) of a 1M solution (c1) in 100ml(v2) the final concentartion is c2=(c1xv1)/v2 or c2=0.01M

Beware your units if C1 is in %, c2 will be in % and if c1 is in Moles/L so will be c2

Knowing the Molecular weight of your compounds is necessary to convert between Moles and %

Patrick

Science has proof without any certainty. Creationists have certainty without
any proof. (Ashley Montague)

ok so i think i get that formula ... but how does moles then relate to percentage. so like for lactose it has a molecular weight of 132 (roughly) and the only formulas im thinking of include n=m/M and c=n/v .... but i don't know how that relates to percentages?

percentages are usually given v/v(volume to volume ratio) or w/v(or weight to volume ratio).

-The first is used for liquids (water, ethanol, detergent like triton...) and is the ratio of the substance to the solvent. i.e. a 13% v/v ethanol solution (aka wine) contains 13ml of ethanol for a final volume of 100ml

-The later is used for solids (salts, sugar,...) and represent the weight of solute(in grams) in a 100ml final solution. i.e. a 10% solution of arabinose contains 10g of arabinose in a 100ml volume. This is the kind of thing you are dealing with.

Now since you can calculate the number of moles in your solution since you know the amount of your solute and its molecular weight, you will have no problem calculating your concentrations (remember 100ml =/= 1L)

Patrick

Science has proof without any certainty. Creationists have certainty without
any proof. (Ashley Montague)

as you wrote, you have n = c.Vso, if you dilute your solution, you add only pure solvent and thus the amount of your solute is not changing, thus if n1 is the amount before dilution and n2 after dilution, it is n1 = n2 and thus you can write c1 . V1 = c2 . V2

this is for the moles and mol/dm3, but the same applies for the %, because if it is true, that n1 = n2, than must be true m1 = m2 (if we're talking about the same substance and thus the same Mr;) and since m = c . Vbecause in this case c is in [%] (w/v), that is, as canalon wrote, how many grams you have per 100 ml of solutionso you get again c1 . V1 = c2 .V2(but remember, that both c are in %!)